Due to difference in molecular structure, chemical shift phenomenon is observed in nuclear magnetic resonance signals measured by MRI, where the resonance frequencies are slightly changed. As a method of utilizing this phenomenon, MRS (Magnetic Resonance Spectroscopy) which separates nuclear magnetic resonance signals to obtains spectra of each metabolite, and MRSI (Magnetic Resonance Spectroscopic Imaging) which visualizes spatial signal intensity distribution for each metabolite have bee known in the art.
Typical metabolites of human body which can be detected by MRS or MRSI include choline, creatine, N-acetyl aspartic acid, lactic acid and so on. By using the amount of these metabolites, development of metabolic abnormality diseases such as cancer etc. can be judged and early-stage diagnosis becomes practicable. Further, it becomes possible to conduct diagnosis of malignancy of tumor without imparting damage to human body.
Since NMR signals of metabolites in human body have an intensity of about 1/1000 of water molecules in human body, they are embedded in water signals and generally cannot be detected. In order to measure signals of the metabolites, there has been proposed a method of suppressing unnecessary signals of water or fat. For example, in a technique disclosed in Patent Document 1, unnecessary signals are suppressed beforehand using a pulse having a frequency band similar to that of unnecessary signals so that the metabolites signals residing in periphery of water signal peek are detect. Such a method of suppressing signals by pseudo saturation of frequency region including resonance frequency of the unnecessary signals is called CHESS (CHEmical Shift Selective).    Patent Document 1: Japanese Patent Application Publication No. S60-168071
In the CHESS, while a single pulse (CHESS pulse) may be used for pseudo saturation, three pulses are generally used in combination with spoiler gradient magnetic fields of three axis directions. In order to sufficiently suppress water signals to keep metabolites from embedded in water signals in CHESS, it is important to irradiate the CHESS pulse with an appropriate amplitude (flip angle). Examples of a method for adjusting the appropriate pulse amplitude are as follows:
(1) Manual adjustment by user
(2) Semi-auto adjustment where a user determines an optimal value from the result of auto-measurement.
(3) Full-auto adjustment where both measurement and determination are automated.
In addition, the full-auto adjustment includes, as a typical methods thereof, all-point searching and absolute value fitting.